Flowering of the reference legume
Arbuscular mycorrhizal fungi help their host plant in the acquisition of nutrients, and this association is itself impacted by soil nutrient levels. High phosphorus levels inhibit the symbiosis, whereas high nitrogen levels enhance it. The genetic mechanisms regulating the symbiosis in response to soil nutrients are poorly understood. Here, we characterised the symbiotic phenotypes in four
- Award ID(s):
- 2139351
- NSF-PAR ID:
- 10367802
- Publisher / Repository:
- Wiley-Blackwell
- Date Published:
- Journal Name:
- The Plant Journal
- Volume:
- 110
- Issue:
- 2
- ISSN:
- 0960-7412
- Page Range / eLocation ID:
- p. 513-528
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
SUMMARY Medicago truncatula is promoted by winter cold (vernalization) followed by long‐day photoperiods (VLD) similar to winter annual Arabidopsis. However, Medicago lacksFLC andCO , key regulators of Arabidopsis VLD flowering. Most plants have twoINHIBITOR OF GROWTH (ING ) genes (ING1 andING2 ), encoding proteins with an ING domain with two anti‐parallel alpha‐helices and a plant homeodomain (PHD) finger, but their genetic role has not been previously described. In Medicago,Mting1 gene‐edited mutants developed and flowered normally, but anMting2‐1 Tnt1 insertion mutant and gene‐editedMting2 mutants had developmental abnormalities including delayed flowering particularly in VLD, compact architecture, abnormal leaves with extra leaflets but no trichomes, and smaller seeds and barrels.Mting2 mutants had reduced expression of activators of flowering, including theFT ‐like geneMtFTa1 , and increased expression of the candidate repressorMtTFL1c , consistent with the delayed flowering of the mutant.MtING2 overexpression complementedMting2‐1 , but did not accelerate flowering in wild type. The MtING2 PHD finger bound H3K4me2/3 peptides weaklyin vitro , but analysis of gene‐edited mutants indicated that it was dispensable to MtING2 function in wild‐type plants. RNA sequencing experiments indicated that >7000 genes are mis‐expressed in theMting2‐1 mutant, consistent with its strong mutant phenotypes. Interestingly, ChIP‐seq analysis identified >5000 novel H3K4me3 locations in the genome ofMting2‐1 mutants compared to wild type R108. Overall, our mutant study has uncovered an important physiological role of a plantING2 gene in development, flowering, and gene expression, which likely involves an epigenetic mechanism. -
SUMMARY The arbuscular mycorrhizal (AM) symbiosis is characterized by the reciprocal exchange of nutrients. AM fungi are oleaginous microorganisms that obtain essential fatty acids from host plants. A lipid biosynthesis and delivery pathway has been proposed to operate in inner root cortex cells hosting arbuscules, a cell type challenging to access microscopically. Despite the central role lipids play in the association, lipid distribution patterns during arbuscule development are currently unknown. We developed a simple co‐staining method employing fluorophore‐conjugated Wheat Germ Agglutinin (WGA) and a lipophilic blue fluorochrome, Ac‐201, for the simultaneous imaging of arbuscules and lipids distributed within arbuscule‐containing cells in high resolution. We observed lipid distribution patterns in wild‐type root infection zones in a variety of plant species. In addition, we applied this methodology to mutants of the
Lotus japonicus GRAS transcription factor RAM1 and theOryza sativa half‐size ABC transporter STR1, both proposed to be impaired in the symbiotic lipid biosynthesis‐delivery pathway. We found that lipids accumulated in cortical cells hosting stunted arbuscules inLjram1 andOsstr1 , and observed lipids in the arbuscule body ofOsstr1 , suggesting that in the corresponding plant species, RAM1 and STR1 may not be essential for symbiotic lipid biosynthesis and transfer from arbuscule‐containing cells, respectively. The versatility of this methodology has the potential to help elucidate key questions on the complex lipid dynamics fostering AM symbioses. -
Summary Iron is an essential cofactor for symbiotic nitrogen fixation, required by many of the enzymes involved, including signal transduction proteins, O2homeostasis systems, and nitrogenase itself. Consequently, host plants have developed a transport network to deliver essential iron to nitrogen‐fixing nodule cells.
Ferroportin family members in model legume
Medicago truncatula were identified and their expression was determined. Yeast complementation assays, immunolocalization, characterization of atnt1 insertional mutant line, and synchrotron‐based X‐ray fluorescence assays were carried out in the nodule‐specificM. truncatula ferroportinMedicago truncatula nodule‐specific geneFerroportin2 (MtFPN2 ) is an iron‐efflux protein. MtFPN2 is located in intracellular membranes in the nodule vasculature and in inner nodule tissues, as well as in the symbiosome membranes in the interzone and early‐fixation zone of the nodules. Loss‐of‐function ofMtFPN2 alters iron distribution and speciation in nodules, reducing nitrogenase activity and biomass production. Using promoters with different tissular activity to driveMtFPN2 expression inMtFPN2 mutants, we determined that expression in the inner nodule tissues is sufficient to restore the phenotype, while confiningMtFPN2 expression to the vasculature did not improve the mutant phenotype.These data indicate that MtFPN2 plays a primary role in iron delivery to nitrogen‐fixing bacteroids in
M. truncatula nodules. -
Abstract l ‐Tyrosine (Tyr) is an aromatic amino acid synthesized de novo in plants and microbes downstream of the shikimate pathway. In plants, Tyr and a Tyr pathway intermediate, 4‐hydroxyphenylpyruvate (HPP), are precursors to numerous specialized metabolites, which are crucial for plant and human health. Tyr is synthesized in the plastids by a TyrA family enzyme, arogenate dehydrogenase (ADH/TyrAa), which is feedback inhibited by Tyr. Additionally, many legumes possess prephenate dehydrogenases (PDH/TyrAp), which are insensitive to Tyr and localized to the cytosol. Yet the role of PDH enzymes in legumes is currently unknown. This study isolated and characterizedTnt1 ‐transposon mutants ofMtPDH1 (pdh1 ) inMedicago truncatula to investigate PDH function. Thepdh1 mutants lackedPDH transcript and PDH activity, and displayed little aberrant morphological phenotypes under standard growth conditions, providing genetic evidence thatMtPDH1 is responsible for the PDH activity detected inM. truncatula . Though plant PDH enzymes and activity have been specifically found in legumes, nodule number and nitrogenase activity ofpdh1 mutants were not significantly reduced compared with wild‐type (Wt) during symbiosis with nitrogen‐fixing bacteria. Although Tyr levels were not significantly different between Wt and mutants under standard conditions, when carbon flux was increased by shikimate precursor feeding, mutants accumulated significantly less Tyr than Wt. These data suggest that MtPDH1 is involved in Tyr biosynthesis when the shikimate pathway is stimulated and possibly linked to unidentified legume‐specific specialized metabolism. -
Summary Plant ‐specific lysin‐motif receptor‐like kinases (LysM‐RLKs) are implicated in the perception of
N ‐acetyl glucosamine‐containing compounds, some of which are important signal molecules in plant−microbe interactions. Among these, both lipo‐chitooligosaccharides (LCOs) and chitooligosaccharides (COs) are proposed as arbuscular mycorrhizal (AM) fungal symbiotic signals. COs can also activate plant defence, although there are scarce data about CO production by pathogens, especially nonfungal pathogens.We tested
Medicago truncatula mutants in the LysM‐RLK MtLYK9 for their abilities to interact with the AM fungusRhizophagus irregularis and the oomycete pathogenAphanomyces euteiches . This prompted us to analyse whetherA. euteiches can produce COs.Compared with wild‐type plants,
Mtlyk9 mutants had fewer infection events and were less colonised by the AM fungus. By contrast,Mtlyk9 mutants were more heavily infected byA. euteiches and showed more disease symptoms.Aphanomyces euteiches was also shown to produce short COs, mainly CO II, but also CO III and CO IV, and traces of CO V, bothex planta andin planta .MtLYK9 thus has a dual role in plant immunity and the AM symbiosis, which raises questions about the functioning and the ancestral origins of such a receptor protein.